Rotary fuel pumps driven by an electric motor have been utilized in fuel delivery systems to deliver fuel under pressure to an internal combustion engine. The pump and power unit are frequently in a common housing mounted in the fuel tank of the vehicle as shown, for example, in U.S. Pat. No. 4,401,416. During operation, a fuel pump will produce a humming noise and especially under higher fuel demands, this noise may be audible to passengers in the vehicle and thus, it is desirable to minimize the noise level of an operating fuel pump.
During the pumping cycle, as one pumping cell is exhausting fuel another cell is taking in fuel at the same time. It has been noted that pressure waves or pulses are present at the inlet cell as well as the outlet cell at all operating pressures and these pressure pulses increase the operating noise of the fuel pump. This increases as the output pressure requirement of the fuel pump is increased due to the increased pressure differential across the pump which increases the magnitude of the dynamic pressure pulses of the fuel. Under increased output pressure requirements, the outlet of the fuel pump can be operating at an average pressure on the order of 60 psig or more while the inlet is usually at an average pressure close to atmospheric. In addition to the noise at increased pressure differentials, the pressure pulses effect the delivery of the fuel from the fuel pump by creating pulses of fuel from the outlet of the fuel pump rather than a smooth flow of the fuel from the pump.